FS8108

Page 8

Jan 2003

Phase/Frequency Detector (PFD)

The PFD compares an internal input frequency divider output signal, f

reference frequency divider output signal, f

proportional to the phase error between f

a passive filter as shown in Fig. 3.

The input/output waveforms for the PFD are shown in Fig. 4.

Fig. 3 – Passive low-pass filter circuit

Fig. 4 – PFD input/output waveforms

DO

to VCO

R1

R2

C

high-Z

high-Z

high-Z

f

R

f

V

DO

LD